Leacture three limb bud formation

Question 1

what are the three parts of a limb (p to D)

Answer 1

stylopod, zeygopod, autopod

Question 2

when does limb foration start in the chick

Answer 2

3 days

Question 3

when does kimb formation start in the mouse and when is it formed

Answer 3

10 daysto 14 days

Question 4

where doe the limb bud form

Answer 4

junctin between the dorsal and ventral ecotderm

in distinct position along the AP axis

Question 5

what experiment shows the AP axis is established very early

Answer 5

take presomiic mesoderm and graft back in incerted = somites form in reverse order
this shows cells have been predetermined with their positional identity

Question 6

how is fgf8 expressed

Answer 6

gradientwith highest at the posterior

Question 7

what is the expression attern of retinoic acid

Answer 7

is highest in the mid trunk of the embryo and declines both posteriorally and anteriorally

Question 8

what is the role of the fgf8 and RA gradients

Answer 8

give positional identity to cells along the AP axis

an address of where they are on it

Question 9

what other signally are also important in establishing the AP axis

Answer 9

WNts and BMPS expressed in posterior (WNT and BMPantagonists expressed in anterior)

Question 10

what is th eoutcome of the signalling gradients

Answer 10

RA/WNT3a and fgf8 activate TF (cdcxs) these then activate Hox genes
hox genes inv in AP patterning

Question 11

what are properties of HOx genes

Answer 11

homeotic TFs
evolutionary conserved
show colinearity
in their order along the chromosome and spatial/temporal pattern along the AP axis

Question 12

where are 3’ hox genes expressed

Answer 12

at the anterior

Question 13

what do the expression pattern of Hoxb genes show

Answer 13

shows anterior borders are distinct whilst posterior are not

Question 14

how does hox expression explain the difference in the number of cervical vertebrae on the mouse

Answer 14

the chick has twice as many as mouse

has a bigger hox 5 expression (=hox5/6 boundary is change in the type of rib)

Question 15

what does hox expression in the snake show

Answer 15

doesnt allow for limbs
as norm region anterior to hoxc6 becomes forelimb
in snake hoxc6 expressed thoroughout - no anterior region of its expression = no limb
expansion of hoxc6 and hoc8 expression correlates with the expasion of thoracic identitiy of skeleton as no act of necessary signalling pathways

Question 16

what is the role of fgf10 and how was this shown

Answer 16

in lpm
initiates limb bud formation
is expressed in the correct areas jus tprior to fomation
ectopic expression induces and ectopic limb
ko = no limb = is necessary

Question 17

what is the TF that activates fgf10

Answer 17

Tbx5

Question 18

what controls the position of fgf10

Answer 18

tbx5 activation
tbx5 expression is activated by the rostral hox code (hox4/5)
and tbx5 expression is repressed by caudal hox code expression

Question 19

where does the fgf10/hox/tbx signalling occur

Answer 19

in the lateral plate mesoderm

Question 20

what does fgf10 induce in the ectoderm of the limb bud

Answer 20

fgf8 expression

Question 21

what TF is expressed in the forelimb bud

Answer 21

tbx5

Question 22

what TF are expressed in the hindlimb bud

Answer 22

Tbx4 and Pitx1

Question 23

what does inducing an ectopic limb etween the two normal limb buds with a fgf10 bead show

Answer 23

in the ectopic limb there is chimeric expression of the tbx gnees = this is consistent with these genes being progeitors for the HL and FL

Question 24

in the chick what is the consequence of tbx4 overexpression and what is the consequence of tbx5 overexpression

Answer 24

tbx4 takes on HL identity (wt= FL)

tbx5 takes on FL identity (wt= HL)

Question 25

what do the overexpression expreiments of tbx genes in the chick show

Answer 25

confirms their role in the FL/HL identitiy

Question 26

what occurs in the mouse if KO the tbx genes

Answer 26

tbx4 - defect in hl

tbx5 - defect in fl

Question 27

what do conditional ko and rescue of tbx4 show

Answer 27

(KO tbx5 then put in tbx4) shows that tbx4 is not sufficient to give hindlimb identity in the mouse = ptype still resemble FL

Question 28

what do experiments with pitx1 show

Answer 28

misexpress in fl gives more hl id
ko = loss of hl feature
when do condtional ko of tbx5 then save with pitx1 = no limb = not sufficient
conditonal ko of tbx5 then rescue with tbx4 and pitx1 = partial hl therefore both imp for fl id

Question 29

what signalling pathway group do fgf belong to ?

Answer 29

tyrosine receptor kinases